Electrostatic actuators are well known for use in a variety of applications, such as, in fluid ejectors for ink jet recording or printing devices. Electrostatic actuators often comprise one or more membranes which can be deflected using electrostatic forces.
FIG. 1 illustrates one example of an electrostatically actuated diaphragm. 10 in a relaxed state. Diaphragm 10 can comprise a substrate 12, an insulator layer 14, a stationary electrode 16, a second insulator layer 18 and a membrane 20. Substrate 12 can be, for example, a silicon wafer. Insulator layers 14 and 18 can be, for example, thin film insulators, such as, silicon nitride. Stationary electrodes 16 and 20 may comprise, for example, a metal or a doped semiconductor, such as doped polysilicon.
Membrane 20 may also comprise a conductive landing post 22, which often comprises the same material as membrane 20, such as metal or a doped semiconductor. Landing post 22 can aid in reducing problems with stiction, which is a common failure mode in electrostatic actuators, where two surfaces that come into contact become permanently attached by Van der Waals forces. Because landing post 22 reduces the amount of surface area that can come into contact, stiction forces are decreased.
In operation, a voltage potential is applied to the stationary electrode 16, which attracts membrane 20 and causes it to deflect, as illustrated in FIG. 2. When fully deflected, landing post 22 can touch insulator layer 18, causing a reduction in the gap between the electrodes. The reduction in the gap often creates high electric fields that can lead to dielectric breakdown, lifetime degradation and other negative performance effects.